1. Field of the Invention
This invention relates generally to casters for use in rollably supporting heavy or large objects--such as machinery or freight--on a floor, and more particularly to such casters that can be locked to prevent rolling when rolling is not desired.
2. Prior Art
Previous lockable casters have provided spring-loaded brake shoes biased or jammed against an internal wheel surface, or cam-type structures which wedge themselves against the outsides of the caster wheels.
Such devices, while very useful, have several limitations. The brake shoes or cams, and their mating wheel surfaces, are subject to wear--which can over the course of time shift the point int he locking action at which reliable locking actually occurs. Such a shift, in turn, can produce unexpected failures of locking action, and thereby extensive and expensive damage to the equipment or other supported objects.
Locking or unlocking some such devices requires undesirably large amounts of force. Applying force to the wheels as is done by some of the prior-art devices has a tendency to deface the outer surfaces of the wheels, making the casters unsightly; or to warp the wheels or damage their axles or bushings, thereby interfering with smooth rolling action (or with smooth pivoting action of the caster about a vertical axis) and sometimes causing objectionable scuffing of the floor.
Many of the prior-art devices make use of mechanical configurations in which the locking force is borne entirely by the mechanism which moves the brake shoe or cam into place against the wheel. If the supported equipment or other object is then forcefully shoved, the braking or camming mechanism can be damaged beyond repair, and the whole caster must then be replaced.
The present invention has as its objectives the elimination of these limitations, through provision of a caster which is positive-locking even after considerably usage and wear has occurred. The invention thus is directed to avoiding unexpected locking failures, avoiding defacement of the wheels and damage to axles or bushings, and avoiding using the actuating mechanism to bear the entire load of the locking forces. Further, the invention aims to provide for replacement of relatively inexpensive parts if the load is shoved with such great force that the positive-locking mechanism is damaged.